Forming a dielectric layer using a hydrocarbon-containing precursor

ABSTRACT

In one embodiment, the present invention includes introducing a precursor containing hydrocarbon substituents and optionally a second conventional or hydrocarbon-containing precursor into a vapor deposition apparatus; and forming a dielectric layer having the hydrocarbon substituents on a substrate within the vapor deposition apparatus from the precursor(s). In certain embodiments, at least a portion of the hydrocarbon substituents may be later removed from the dielectric layer to reduce density thereof.

BACKGROUND

The present invention relates to forming layers on a substrate and moreparticularly to forming a dielectric layer using ahydrocarbon-containing material.

Semiconductor devices typically include metal layers that are insulatedfrom each other by dielectric layers. It is desirable that thesedielectric layers which are made of an insulative material have arelatively low dielectric constant. While such dielectric layers may bemade of various materials, silicon dioxide is one material used, howeverit has a higher dielectric constant than is desired for forming advancedsemiconductor devices. One material used to provide a low dielectricconstant (K_(eff)) is a carbon doped oxide (CDO). Typically, CDO filmsare formed using a vapor deposition process. It is desirable however, toobtain a dielectric layer having a lower K_(eff) than possible usingconventional vapor deposition processing and precursor materials.

Certain materials used as dielectric films may be instead formed using aspin-on process. While such spin-on materials may have a relatively lowK_(eff), they typically have poor mechanical strength and may sufferfrom structural integrity problems during subsequent processing. Thusthere is a need for a dielectric layer that has reliable mechanicalstrength for subsequent processing and a relatively low dielectricconstant upon device completion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A–1B are chemical structures of substituted precursors inaccordance with various embodiments of the present invention.

FIGS. 2A–2C are chemical structures of substituted precursors inaccordance with various embodiments of the present invention.

FIGS. 3A–3E are chemical structures of substituted precursors inaccordance with various embodiments of the present invention.

FIG. 4 is an example plasma enhanced chemical vapor deposition reactionin accordance with one embodiment of the present invention.

FIGS. 5A–5B are chemical structures of substituted precursors inaccordance with several embodiments of the present invention.

FIG. 6 is an example plasma enhanced chemical vapor deposition inaccordance with a second embodiment of the present invention.

DETAILED DESCRIPTION

In one embodiment of the present invention, a dielectric layer may bedeposited using a hydrocarbon substituted silicon-based precursor (a“substituted precursor”). In various embodiments, the hydrocarbonsubstituents may vary in chain length, branching, sterics, C/H ratio,heteroatoms and other chemical attributes to control resulting materialcomposition and engineering properties (e.g., activation energy (E_(a)),carbon to silicon (C/Si) ratio, rate of degradation, and K_(eff)). Insome embodiments, large hydrocarbon substituents may act as porogenicfunctional groups.

In other embodiments, a percentage of a substituted precursor may beco-deposited with conventional silicon oxide and CDO precursor(s)(hereafter “conventional precursors”), which include, but are notlimited to tetraethylorthosilicate (TEOS), TOMCATS,dimethyldimethoxysilane (DMDMOS), and OMCTS. The percentage ofsubstituted precursor to conventional precursor may vary from a minimalamount (e.g., less than 5%) to 100%. This percentage may vary based uponthe morphology, mechanical strength, C/Si ratio, and/or the porogeniccharacteristics desired of the dielectric film. In certain embodiments,the percentage of substituted precursor to conventional precursor may bebetween approximately 10% to approximately 50%.

After deposition of the dielectric layer, various subsequent processingmay be performed. For example, metal interconnects may be formed in oron the dielectric layer via a dual damascene or other process. After thedesired subsequent processing has been completed, the hydrocarbonfunctionality of the substituted precursors may be removed (hereafterreferred to as “post-treatment”) to form a dielectric layer with greaterporosity and a lower dielectric constant. While the dielectric constantobtained may vary in different embodiments, in certain embodiments, thedielectric constant may be reduced to below 3.0 and even 2.5. More so,in embodiments in which the substituted precursor includes a largemoiety, the dielectric constant may be reduced to approximately 2.0.

In different embodiments, a dielectric layer may be deposited usingvarious techniques, including for example physical vapor deposition(PVD), chemical vapor deposition, (CVD), or plasma enhanced chemicalvapor deposition (PECVD). One example deposition may be thermaldeposition of a substituted precursor with a conventional molecularprecursor such as TEOS, TMOS, and the like. Similarly, deposition may beaccomplished via plasma assisted deposition of a substituted precursorwith a molecular precursor such as TEOS, DMDMOS, and the like.Alternately, the reaction of a substituted precursor and a silane-basedprecursor with an oxygen source (such as oxygen or water), or a mixtureof any of the above techniques may be used to deposit the dielectriclayer (e.g., an interlayer dielectric (ILD)).

Deposition of the dielectric layer may be accomplished using aconventional reaction chamber operating at conventional temperatures andpressures. In certain embodiments, the thickness of the depositeddielectric layer may be between approximately 100 Angstroms andapproximately 10,000 Angstroms.

In certain embodiments, the substituted precursor may be engineered totake up additional space in the CDO lattice and modulate its engineeringproperties (including K_(eff), decomposition temperature, decompositionspeed, E_(a), mechanical strength, porosity, pore structure, filmuniformity, modulus, hardness, adhesion, cohesive strength, and thelike).

Design of a substituted precursor may follow one of several designmotifs in accordance with various embodiments of the present invention.In one embodiment, depicted in FIG. 1A, the substituted precursor mayhave the general formula [R₂]_(4−x)Si[R₁]_(x), where x equals one, two,or three; R₁ may be a functional group that forms Si—O bonds duringdeposition (i.e., a silanating/alkoxy silanating functional group), forexample, H, a halogen, OCH₃, OCH₂CH₃, or an alkoxy; and R₂ may provideporogen functionality via a bulky carbon-based functional group, forexample, norbornyl, neopentyl, adamantyl, cyclopentadienyl, methyladamantyl, an alicyclic, a heterocyclic, a branched alkyl, a straightchain alkyl, or an aromatic. In the case of x=1 (a single silanatinggroup), more than one precursor may be used to build the film to promotebonding between precursor molecules during the deposition process.

In another embodiment, depicted in FIG. 1B, the substituted precursormay have the general formula [R₂X]_(4−x)Si[R₁]_(x), where X is aheteroatom, such as O, N, or S, for example; and x, R₁ and R₂ may be asabove.

In still another embodiment, the substituted precursor may have thegeneral formula [R₂]_(x)Si[R₁]_(y), where R₁, R₂ and x are as above andy is one or two, depending on the value of x.

Referring now to FIGS. 2A–2C, shown are example substituted precursorsfor use in forming dielectric layers in accordance with variousembodiments of the present invention. As shown in FIG. 2A, in oneembodiment a substituted precursor may be norbornyl trimethoxysilane. Asshown in FIG. 2B, in a second embodiment a substituted precursor may beadamantyl trimethoxysilane. As shown in FIG. 2C, in a third embodiment asubstituted precursor may be dicyclopentadienyl trimethoxysilane. Inother embodiments, substituted precursors may includetrietoxynorbornylsilane, tethered cage, substituted cage(2-methyl-2-(triethoxysilyl)norbornane), aryl functionality (benzyl andphenyl), straight chain, and branched chain, and fluorocarbonsubstitutions. More so, derivatives or analogs of these compounds mayalso be used as substituted precursors in certain embodiments.

While the silicon content of the precursors of FIGS. 2A–2C is shown assingle silicon atoms, it is to be understood that in other embodimentsdimeric and oligomeric species, such as disilanes, diazides,silsesquioxanes and others, may be used. Hydrocarbon substituents mayhave many possible substitution patterns in such multinuclear systems.

Heteroatom substituents may serve several functions, including directionof plasma activation and energy transfer during deposition, promotion ofreactivity at specific locations, as well as modulation of decompositionrate and mechanism, and the thermal and mechanical properties of thedeposited film. Examples of heteroatoms and functionality includehalogen, nitrogen, nitro group, diazo group, and azo group, for example.

In certain embodiments, films may be deposited using multiplesubstituted precursors having differing activation energies fordegradation and differing amounts of hydrocarbon bulk available forloss. Referring now to FIGS. 3A–3E, shown are example substitutedprecursors for use in forming dielectric layers in accordance with otherembodiments of the present invention. As shown in FIG. 3A, in oneembodiment a substituted precursor may be tertbutoxy trimethoxysilane.As shown in FIG. 3B, in a second embodiment a substituted precursor maybe isoproxy trimethoxysilane. As shown in FIG. 3C, in a third embodimenta substituted precursor may be alpha methyl norbornyloxytrimethoxysilane. As shown in FIG. 3D in a fourth embodiment asubstituted precursor may be norbornyl oxytrimethoxysilane. As shown inFIG. 3E, in a fifth embodiment a substituted precursor may be adamantylmethoxy trimethoxysilane. As shown in FIGS. 3A–3E, the hydrocarbons arebound to the silicon through a linker moiety (e.g., oxygen). In otherembodiments, other derivatives or analogs may be bound to the silicon.

In certain embodiments in which post-treatment of a single precursor isperformed, the precursor may have multiple different hydrocarbonfunctionalities. In one embodiment, two of these sites may be silanatingfunctional groups to form the silicon-oxygen backbone of the dielectriclayer, while a third site may be an organic functional group that isdesired to be incorporated into the dielectric layer, and a fourth sitemay be a sacrificial functional group. Such a precursor is depicted inFIG. 4.

For example, in one embodiment two alkoxy groups may be attached to formthe silicon-oxygen backbone. In this example, a third site may be afunctional group that attaches to the silicon molecule at one or twopoints (denoted by R in FIG. 4). For example, a ring structure, such asa tetra-substituted carbon in the beta position or another structurestabilized against beta-hydride elimination may be used. As an example,FIG. 5A depicts a norbornyl-functionalized trimethoxysilane, and FIG. 5Bdepicts a β,β-dimethylnorbornyl trimethoxysilane, which is stabilizedagainst beta-hydride elimination. This third site may be a stericallylarge molecule. In other embodiments, this third site may be anelectron-accepting functional group, for example, a phenyl group, suchas a benzene ring, or an amide group having a conjugated double bond oran alternating double bond single bond structure. Alternately the thirdsite may be a polydentate ligand or other functional group which ismultiply bonded to the silicon atom. Examples of such ligands include,but are not limited to, 2,4-pentanedioate (acetyl acetonate; acac),2,2,6,6-tetramethyl-3,5-heptanedionate (thd), dipivaloylmethane (dpm),and bipyridine (bpy).

In various embodiments, a fourth site attached to the silicon moleculemay be, for example, an alkoxy, an alkyl, a sacrificial functional groupor the same functional group chosen for the third site (denoted as X inFIG. 4).

In one embodiment, the third and fourth sites may be functional groupshaving different reaction pathways. For example, one functional groupmay be very reactive and be the primary reaction pathway for monomeractivation and subsequent film deposition, in accordance with the schemedepicted in FIG. 4. The second functional group may be large andunreactive so that it may be incorporated into the film and may beselected to avoid common plasma reaction pathways, such as beta hydrideelimination or hydrolysis, in certain embodiments. In certainembodiments, sacrificial components that decompose preferentially mayinclude, but are not limited to, halogens, olefins, functional groupshighly susceptible to beta-hydride elimination such as ethyl or ethoxygroups, or other functional groups (e.g., a precursor with two differentorganic functional ethoxy groups, either of which may be susceptible topost-treatment if incorporated into the film).

In an embodiment in which an Si-based organic precursor is reacted withan oxidizing agent, reactions may be modulated by steric hindrance ofsurface reactions or by electronic effects of substituents groups. Insuch an embodiment, Si—H or Si—R (where R is a small functional group)may be susceptible to attack by water (i.e., hydrolysis) to create a newhydroxyl group, which can act as an active site for film growth.Alternately, a much larger functional group that can block access toreactive sites will not react and will be incorporated into the film.Thus, surface reactions of the film may be prevented during film growth,enabling incorporation of organic porogens which may be later removedfrom the film. In addition to the organic precursors described above,hydroxyl-substituted functional groups may also be used (such groups maybe chemically bound to the film at more than one site).

As discussed above, in one embodiment the precursor may be stabilizedduring deposition by adding a sacrificial functional group that willfragment preferentially during decomposition, leaving the rest of themolecule (including the organic porogen) intact. Such a precursor mayhave the sacrificial functional group attached directly to the silicon(shown as X in FIG. 4) or attached to the organic portion (also shown asX in FIG. 6).

Referring now to FIG. 4, shown is an example PECVD reaction inaccordance with one embodiment of the present invention. As shown inFIG. 4, a silicon molecule has four sites attached thereto, namely twoalkoxy groups, a third site which is a functional group (R) desired tobe incorporated into the dielectric film, and a fourth site which is asacrificial functional group (X). In one embodiment, X may be afunctional group which is especially labile under plasma depositionconditions, such as a halogen, an olefin (e.g., a vinyl group), or amoiety susceptible to beta-hydride elimination (e.g., an ethyl group).As shown in FIG. 4, the sacrificial functional group (shown as X* afterthe reaction) is not incorporated into the dielectric film.

Referring now to FIG. 6, shown is an example PECVD reaction inaccordance with a second embodiment of the present invention. As shownin FIG. 6, a silicon molecule has four sites attached thereto. In thisembodiment, in addition to the two alkoxy groups, a methyl group and anorganic moiety (e.g., the benzene ring shown in FIG. 6) are attacheddirectly to the silicon molecule. In this embodiment, the sacrificialfunctional group (X) is attached to the organic moiety, rather than thesilicon molecule itself. As discussed above with regard to FIG. 4, Xrepresents a functional group which is especially labile under plasmadeposition conditions. As shown in FIG. 6, the sacrificial functionalgroup (shown as X* after the reaction) is not incorporated into thedielectric film. While FIG. 6 shows a sacrificial group attached to anaromatic functionality which is attached directly to the silicon, otheraromatic groups or non-aromatic groups may be used and thus incorporatedinto the film during deposition.

In one embodiment, reaction conditions may be chosen so that thereaction/decomposition of one functional group is much faster than theother so that organic functional groups may be included in the film.These groups may be removed during later post-treatment to reduce thedielectric constant of the film.

In one embodiment, the dielectric layer may be used as a substrate fordesired subsequent processing. For example, a dual damascene process maybe performed to form metal interconnects in the dielectric layer.

Certain embodiments of the present invention may provide hydrocarbonbulk for loss, and subsequent removal of the hydrocarbon bulk mayincrease the porosity of the dielectric layer. When the porosity of thedielectric layer increases, the K_(eff) decreases. The stoichiometry ofthe original film (and thus the ratio of precursors) depends upon thedesired final K_(eff).

In one embodiment, after the metal stack (i.e., metal interconnect) iscomplete, the dielectric layer may be subjected to an additional process(the aforementioned “post-treatment”) to remove the hydrocarbonsubstitutions in the matrix (and the accompanying bulk). However, it isto be understood that in other embodiments, hydrocarbon removal mayoccur at other points in the process flow, such as after chemicalmechanical planarization, if a particular integration scheme dictates.

In one embodiment, thermal decomposition may be employed to remove thesubstituted precursor. In certain embodiments, the thermal removal mayoccur at temperatures between approximately 200°Celsius (C.) andapproximately 500° C. The duration of such thermal removal may also varyin different embodiments, and may range from approximately one minute toapproximately two hours, in certain embodiments.

All or substantially all of the substituted precursor may be removed toprovide for increased porosity in one embodiment. However, in otherembodiments, particularly where the substituted precursor includes alarge cage, for example, a methyl-based precursor, a greater portion ofthe substituted precursor (i.e., the methyl group) may remain in thedielectric layer after the removal process.

The removal process may be aided by a photo-acid generator or othercatalysts in certain embodiments. For example, an acid or other catalystmay be co-deposited with the precursors which may later aid in removalof the substituted precursor. Such acids may include Lewis and Brønstedacids, for example.

In other embodiments, the removal process may include a plasma etch orashing process. Such etching or ashing may be performed usingconventional parameters and materials.

While the above embodiments relate to substituted precursors, it is tobe understood that in certain embodiments, hydrocarbon substitutedstructures may be in a polymer or oligomer form and may be co-deposited(along with conventional polymers or oligomers) on a substrate via aspin-on technique.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A method comprising: forming a dielectric layer on a substrate, thedielectric layer comprising hydrocarbon substituents; forming at leastone metal interconnect in the dielectric layer; and removing at least aportion of the hydrocarbon substituents from the dielectric layer usingcatalyst comprising an acid to reduce density of the dielectric layerafter forming the at least one metal interconnect.
 2. The method ofclaim 1, further comprising reducing a dielectric constant of thedielectric layer by removing at least the portion of the hydrocarbonsubstituents.
 3. The method of claim 1, wherein the hydrocarbonsubstituents comprise at least one carbon-based group.
 4. The method ofclaim 1, further comprising obtaining the hydrocarbon substituents froma precursor having a formula [R2]4−xSi[R1]x, wherein R1 comprises afunctional group to form Si—O bonds during deposition, wherein R2comprises a carbon-based group, and wherein x equals one, two, or three.5. The method of claim 1, further comprising forming the dielectriclayer including the catalyst.
 6. A method comprising: introducing afirst precursor into a vapor deposition apparatus; introducing a secondprecursor into the vapor deposition apparatus, the second precursorcomprising a silicon-based precursor including hydrocarbon substituents;introducing a catalyst into the vapor deposition apparatus; forming adielectric layer having the hydrocarbon substituents and the catalyst ona substrate within the vapor deposition apparatus from the firstprecursor, the second precursor, and the catalyst; forming at least onemetal interconnect in the dielectric layer; and thereafter removing atleast a portion of the hydrocarbon substituents from the dielectriclayer to reduce density of the dielectric layer using the catalyst. 7.The method of claim 6, further comprising introducing the secondprecursor in an amount of less than fifty percent of the firstprecursor.
 8. The method of claim 6, further comprising introducing thesecond precursor having a formula [R2]4−xSi[R1]x, wherein R1 comprises afunctional group to form Si—O bonds during deposition, wherein R1comprises a carbon-based group, and wherein x equals one, two, or three.9. The method of claim 8, wherein the functional group is selected fromthe group consisting of H, a halogen, OCH3, OCH2CH3, and an alkoxy. 10.The method of claim 8, wherein the carbon-based group is selected fromthe group consisting of norbornyl, neopentyl, adamantyl,cyclopentadienyl, methyl adamantyl, an alicyclic, a heterocyclic, abranched alkyl, a straight-chain alkyl, and an aromatic.
 11. The methodof claim 8, wherein the carbon-based group is beta-substituted.
 12. Themethod of claim 6, further comprising introducing the second precursorhaving a formula [R2X]4−xSi[R1]x, wherein X comprises a heteroatom, R1comprises a functional group to form Si—O bonds during deposition,wherein R2 comprises a carbon-based group, and wherein x equals one,two, or tree.
 13. The method of claim 12, wherein the functional groupis selected from the group consisting of H, a halogen, OCH3, OCH2CH3,and an alkoxy.
 14. The method of claim 12, wherein the carbon-basedgroup is selected from the group consisting of norbornyl, neopentyl,adamantyl, cyclopentadienyl, methyl adamantyl, an alicyclic, aheterocyclic, a branched alkyl, a straight-chain alkyl, and an aromatic.15. The method of claim 6, farther comprising introducing the secondprecursor having a formula [R2]x Si[R1 ]y, wherein R1 comprises afunctional group to form Si—O bonds during deposition, wherein R2comprises a carbon-based group, and wherein x equals one two, or threeand wherein y equals one or two.
 16. The method of claim 15, wherein thefunctional group is selected from the group consisting of H, a halogen,OCH2CH3, and an alkoxy.
 17. The method of claim 15, wherein thecarbon-based group is multiply bonded to the silicon more than once. 18.A method comprising: introducing a single precursor into a reactionchamber, the single precursor comprising silicon and a sacrificial groupcomprising carbon; introducing a catalyst into the reaction chamber;forming a dielectric layer on a substrate within the reaction chamberusing the single precursor, the dielectric layer including the catalystco-deposited with the single precursor; and removing at least a portionof the sacrificial group from the dielectric layer using the catalyst.19. The method of claim 18, further comprising including a sacrificialfunctional group attached directly to the silicon.
 20. The method ofclaim 18, further comprising including a sacrificial functional groupattached directly to an organic portion of the single precursor.
 21. Amethod comprising: introducing a single precursor into a reactionchamber, the single precursor comprising a first functional groupcomprising an organic porogen and a second functional group; introducinga catalyst into the reaction chamber with the single precursor; forminga dielectric layer having the organic porogen on a substrate within thereaction chamber using the single precursor, the dielectric layerfurther having the catalyst; and forming at least one metal interconnectin the dielectric layer and thereafter removing at least a portion ofthe organic porogen from the dielectric layer to reduce density of thedielectric layer.
 22. The method of claim 21, wherein the secondfunctional group comprises a sacrificial functional group that fragmentsfrom a remaining portion of the single precursor.
 23. The method ofclaim 22, further comprising eliminating the sacrificial functionalgroup via beta-hydride elimination.
 24. The method of claim 21, whereinthe single precursor comprises silicon having a first site, a secondsite, a third site, and a fourth site, wherein a first hydrogen,halogen, or alkoxy group is attached to the first site, a secondhydrogen, halogen, or alkoxy group is attached to the second site, thefirst functional group is attached to the third site and the secondfunctional group is attached to the fourth site.
 25. The method of claim24, wherein the first functional group and the second functional grouphave different reaction pathways.
 26. The method of claim 21, furthercomprising removing at least a portion of the organic porogen using thecatalyst.